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        <h2>
          <span class="refentrytitle">tone</span>
        </h2>
        <p>tone — 
      A first-order recursive low-pass filter with variable frequency response.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp158768928"></a>
        <h2>Description</h2>
        <p>
      A first-order recursive low-pass filter with variable frequency response.
    </p>
        <p>
      <span class="emphasis"><em>tone</em></span> is a 1 term IIR filter. Its formula is:
        </p>
        <div class="informalexample">
          <p>
            y<sub>n</sub> = c1 * x<sub>n</sub> + c2 * y<sub>n-1</sub>
          </p>
        </div>
        <p>

      where

        </p>
        <div class="informalexample">
          <p>
            </p>
          <div class="itemizedlist">
            <ul class="itemizedlist" style="list-style-type: disc; ">
              <li class="listitem">
                <p>b  = 2 - cos(2 π hp/sr);</p>
              </li>
              <li class="listitem">
                <p>c2 = b - sqrt(b<sup>2</sup> - 1.0)</p>
              </li>
              <li class="listitem">
                <p>c1 = 1 - c2</p>
              </li>
            </ul>
          </div>
          <p>
          </p>
        </div>
        <p>
    </p>
      </div>
      <div class="refsect1">
        <a id="idp158777120"></a>
        <h2>Syntax</h2>
        <pre class="synopsis">ares <span class="command"><strong>tone</strong></span> asig, khp [, iskip]</pre>
      </div>
      <div class="refsect1">
        <a id="idp158779328"></a>
        <h2>Initialization</h2>
        <p>
      <span class="emphasis"><em>iskip</em></span> (optional, default=0) -- initial disposition of internal data space. Since filtering incorporates a feedback loop of previous output, the initial status of the storage space used is significant. A zero value will clear the space; a non-zero value will allow previous information to remain. The default value is 0.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp158781264"></a>
        <h2>Performance</h2>
        <p>
      <span class="emphasis"><em>ares</em></span> -- the output audio signal.
    </p>
        <p>
      <span class="emphasis"><em>asig</em></span> -- the input audio signal.
    </p>
        <p>
      <span class="emphasis"><em>khp</em></span> --  the response curve's half-power point, in Hertz. Half power is defined as peak power / root 2. 
    </p>
        <p>
      <span class="emphasis"><em>tone</em></span> implements a first-order recursive low-pass filter in which the variable <span class="emphasis"><em>khp</em></span> (in Hz) determines the response curve's half-power point. Half power is defined as peak power / root 2.
    </p>
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      <div class="refsect1">
        <a id="idp158786064"></a>
        <h2>Examples</h2>
        <p>
      Here is an example of the tone opcode. It uses the file <a class="ulink" href="examples/tone.csd" target="_top"><em class="citetitle">tone.csd</em></a>.
      </p>
        <div class="example">
          <a id="idp158787840"></a>
          <p class="title">
            <strong>Example 934. Example of the tone opcode.</strong>
          </p>
          <div class="example-contents">
            <p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
            <pre class="programlisting">
<span class="csdtag">&lt;CsoundSynthesizer&gt;</span>
<span class="csdtag">&lt;CsOptions&gt;</span>
<span class="comment">; Select audio/midi flags here according to platform</span>
-odac     <span class="comment">;;;realtime audio out</span>
<span class="comment">;-iadc    ;;;uncomment -iadc if realtime audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o tone.wav -W ;;; for file output any platform</span>
<span class="csdtag">&lt;/CsOptions&gt;</span>
<span class="csdtag">&lt;CsInstruments&gt;</span>

<span class="ohdr">sr</span> <span class="op">=</span> 44100 
<span class="ohdr">ksmps</span> <span class="op">=</span> 32 
<span class="ohdr">0dbfs</span>  <span class="op">=</span> 1 
<span class="ohdr">nchnls</span> <span class="op">=</span> 2

<span class="oblock">instr</span> 1

asig <span class="opc">diskin2</span> "beats.wav", 1
     <span class="opc">outs</span> asig, asig
<span class="oblock">endin</span>

<span class="oblock">instr</span> 2

kton <span class="opc">line</span> 10000, p3, 0		<span class="comment">;all the way down to 0 Hz</span>
asig <span class="opc">diskin2</span> "beats.wav", 1
asig <span class="opc">tone</span> asig, kton		<span class="comment">;half-power point at 500 Hz</span>
     <span class="opc">outs</span> asig, asig
<span class="oblock">endin</span>

<span class="csdtag">&lt;/CsInstruments&gt;</span>
<span class="csdtag">&lt;CsScore&gt;</span>

<span class="stamnt">i</span> 1 0 2
<span class="stamnt">i</span> 2 2 2

<span class="stamnt">e</span>

<span class="csdtag">&lt;/CsScore&gt;</span>
<span class="csdtag">&lt;/CsoundSynthesizer&gt;</span>
</pre>
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        <p><br class="example-break" />
    </p>
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      <div class="refsect1">
        <a id="idp158792128"></a>
        <h2>See Also</h2>
        <p>
      <a class="link" href="areson.html" title="areson"><em class="citetitle">areson</em></a>,
      <a class="link" href="aresonk.html" title="aresonk"><em class="citetitle">aresonk</em></a>,
      <a class="link" href="atone.html" title="atone"><em class="citetitle">atone</em></a>,
      <a class="link" href="atonek.html" title="atonek"><em class="citetitle">atonek</em></a>,
      <a class="link" href="port.html" title="port"><em class="citetitle">port</em></a>,
      <a class="link" href="portk.html" title="portk"><em class="citetitle">portk</em></a>,
      <a class="link" href="reson.html" title="reson"><em class="citetitle">reson</em></a>,
      <a class="link" href="resonk.html" title="resonk"><em class="citetitle">resonk</em></a>,
      <a class="link" href="tonek.html" title="tonek"><em class="citetitle">tonek</em></a>
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